1. Field of the Invention
The present invention relates to an information refresh method, storage system and storage medium thereof for re-recording information on a storage medium so as to prevent the disappearance of information on a storage medium, and more particularly, to an information refresh method, storage system and storage medium for re-recording this information by detecting that information, which needs to be refreshed.
2. Description of the Related Art
Remarkable improvements have been made in magnetic record density in recent years. For example, the recording density for hard disk devices, which are used as storage devices in computers and so forth, is doubling annually. In this magnetic recording, to improve write and read characteristics (signal-to-noise ratio (S/N)) even when writing and reading high-density information, the size of the crystal grain of the medium""s data recording film is becoming smaller.
For example, current recording density is 10-gigabits (Gbits) per square inch, but when this recording density becomes around 30 Gbits per square inch, the size of the crystal grain will become extremely small. When this happens, there will occur what is called thermal decay of demagnetization, by which magnetic information is lost due to thermal fluctuation.
For a longitudinal magnetic recording system in particular, since xe2x80x9c1xe2x80x9d, xe2x80x9c0xe2x80x9d information is indicated by the direction of magnetization, when the direction of magnetization changes, recorded data is disappeared. The temperature energy of the magnetic material, and the fact that the inverse magnetic field of the magnetic material itself becomes large when magnetic recording density becomes high density are pointed to as causes of this disappearance of data. To prevent the disappearance of data due to this thermal fluctuation, the re-writing of data, what is called refresh control, becomes necessary.
The capacity of a magnetic disk in a hard disk device is extremely large. For this reason, it takes a long time to re-write all of the information stored thereon. Thus, there is a proposal to make refresh processing time shorter. That is, a method for detecting from among the information on a disk that information which should be refreshed, and refreshing the detected information. In prior, the following methods have been proposed as this method.
(1) First method is a method for recording reference data on a recording medium separately from ordinary data, and making a determination as to whether or not refresh is needed for the corresponding data in accordance with the playback level value of this reference data (For example, Japanese Patent Laid-open No. 10-255202).
(2) Recorded data deteriorates together with the passage of time after writing. Thus, another method is a method for determining whether or not refresh needs by measuring the elapsed time after recording. Or, the other method is a method for performing refresh when a change of temperature of the medium is detected, and the change is large (For example, Japanese Patent Laid-open No. 10-255209).
However, conventional technology has the following problems.
(1) The problem with the first conventional technology is that because the playback level of reference data is detected, it is not possible to determine the actual deterioration of the data. That is, it is known that the thermal fluctuation phenomenon differs in accordance with the recording pattern, but it is not possible to accurately detect data that should be refreshed by detecting the playback level of reference data.
(2) Further, the first conventional technology is also problematic in that an area on which to record reference data must be provided on a recording medium, causing recording area to be wasted.
(3) As for the second conventional technology, since the elapsed time for each data is detected, refresh can be realized relatively easily, but the problem is that because elapsed time indirectly indicates the deterioration of data, in actuality, a determination is made that refresh must be performed even on data that does not need to be refreshed. That is, because re-recording is performed for data that does not require refresh, there is a great likelihood that huge amounts of wasteful processing will take place.
(4) Further, in the second conventional technology, it is also disclosed that data to be refreshed is further clarified by measuring temperature, but the problem is that temperature also indirectly indicates data deterioration, and, in the end, in actuality a determination is made that refresh must be performed even on data that does not need to be refreshed.
(5) Furthermore, in the case of a magnetic disk, because servo information is also magnetically recorded together with data information, the signal quality of the servo information is similarly deteriorated by thermal fluctuations. However, the problem is that when servo information is re-recorded, because this servo information cannot be read, head positioning is not possible, making it substantially impossible to refresh servo information.
(6) Further, for the indirect detection methods of the first and second conventional technologies, the problem is that it is impossible to detect the deterioration of the quality of servo information.
(7) Furthermore, for a high-density medium that requires refresh frequently, the problem is that access is limited by refresh, deteriorating the performance of the storage medium.
An object of the present invention is to provide an information refresh method, storage system and storage medium for accurately determining whether or not information should be refreshed.
Another object of the present invention is to provide an information refresh method, storage system and storage medium for detecting information to be refreshed from actual information.
Yet another object of the present invention is to provide an information refresh method, storage system and storage medium for preventing the wasting of storage area of a storage medium, and for detecting information to be refreshed.
Yet another object of the present invention is to provide an information refresh method, storage system and storage medium for detecting information to be refreshed in accordance with the characteristics of each storage medium.
Yet another object of the present invention is to provide an information refresh method, storage system and storage medium for refreshing servo information via the storage device itself.
Yet another object of the present invention is to provide an information refresh method, storage system and storage medium for accurately determining whether servo information should be refreshed.
Yet another object of the present invention is to provide an information refresh method, storage system and storage medium for not limiting read access even when refresh is performed.
To achieve these objects, an information refresh method of the present invention comprises the step of measuring from head output the playback output level of targeted information of the above-mentioned storage medium, and determining whether or not refresh is necessary, and the step of re-recording the above-mentioned information requiring refresh to the above-mentioned storage medium via the above-mentioned head.
In an aspect of an embodiment of the present invention, the deterioration of data is directly detected by monitoring the playback output level of targeted information. For this reason, it is possible to accurately detect whether or not information should be refreshed, enabling the prevention of useless refresh. Further, because detection is direct, the deterioration of servo information can also be detected, and moreover, there is no need to provide a reference data area on a storage medium, making it possible to prevent a reduction of storage capacity.
In an information refresh method of another aspect of the present invention, the above-mentioned determination step comprises a step for detecting candidate data to be refreshed by measuring the elapsed time from the writing of each data, and a step for determining whether or not to perform refresh by measuring the playback output level of the abovementioned candidate data via the output of the abovementioned head.
In this aspect of the present invention, refresh candidate data is selected based on the elapsed time of data, and data to be refreshed is selected based on the playback output level of the selected candidate data. However, checking the playback output levels of all the data is troublesome and time consuming. Thus, a certain amount of screening is done in advance by providing prior to checking the playback output level a method for selecting refresh candidate data based on the elapsed time of data, which can be performed via a relatively simple process.
Thus, refresh data can be accurately obtained, and, in addition, processing time can also be prevented from taking a long time. Further, since actual data is checked, it is possible to prevent the waste of storage area.
In an information refresh method of another aspect of the present invention, the above-mentioned determination step comprises a step for measuring a first output level of the above-mentioned candidate data via the above-mentioned head, a step for reading out and measuring a second output level of the above-mentioned candidate data after writing the abovementioned candidate data to the above-mentioned storage medium, and a step for determining whether or not the above-mentioned refresh is necessary based on the ratio of the above-mentioned first and second output levels.
In this aspect, to detect the deterioration of data based on data playback output levels, a change in relative levels is checked using a ratio between a readout level and a readout level at rewrite. Thus, level changes can be accurately checked without relying on head or storage medium characteristics.
In a further aspect of the information refresh method of the present invention, the above-mentioned determination step comprises a step for determining whether or not refresh is necessary based on the amplitude of servo information of a relatively long recording wavelength, and the amplitude of servo information of a relatively short recording wavelength from among the servo information, which the above-mentioned head read out.
In this aspect, to make a determination as to whether or not servo information should be refreshed, signal amplitudes within servo information are compared. That is, because the degree of deterioration of signal amplitudes will differ over time according to recording wavelength, the signal degradation of servo information is detected by comparing signal amplitudes. For this reason, first, servo information refresh becomes possible inside the drive. Second, signal degradation can be detected by merely reading servo information, and a servo information write process is not necessary to detect signal degradation. Thus, signal degradation can be detected without sacrificing servo information-based positioning.
In another information refresh method of the present invention, the re-recording step comprises a step for re-recording the servo information of the above-mentioned storage medium while positioning the above-mentioned head using other servo information of the above-mentioned storage medium.
In this aspect, to prevent positioning from becoming unstable in the re-recording of servo information due to the servo information thereof not being able to be read in, positioning is performed by other servo information. In accordance therewith, it is possible to prevent positioning from becoming unstable during the re-recording of servo information, and servo information refresh becomes possible in the drive itself.
The information refresh method of the present invention further has a step for detecting data to be simultaneously written to the data that determines the need for the above-mentioned refresh, and a step for re-recording the above-mentioned detected data on the above-mentioned storage medium using the above-mentioned head.
In this aspect, simultaneously written data is refreshed even without checking as data disappearance is highly likely. Thus, the time required for checking refresh can be greatly shortened.
A separate information refresh method of the present invention comprises a step for reading via a head the information of a storage medium, and thereafter storing the information in memory to prevent the disappearance of the above-mentioned storage medium information, a step for re-recording information on the above-mentioned storage medium via the above-mentioned head, and a step for outputting the above-mentioned memory information as the above-mentioned read data when read access of the information in the above-mentioned re-recording occurs during the above-mentioned re-recording.
In this aspect, the object is to perform constant refresh. Thus, it becomes possible to protect data even on high-density storage media for which heat fluctuation is apt to occur. Further, because re-recorded data is stored in memory, even if there is a read access during re-recording, the access thereof is not delayed. That is, the deterioration of access performance can be prevented even while performing constant refresh.